1. Field of the Invention
The following description relates to a method of transmitting a digital signal, a transmitter, and a method of receiving a transmitted signal in a receiver.
2. Discussion of Related Art
In general, transmission of digital signals has advantages in that it is less sensitive to noise and has less distortion and high transmission efficiency compared to analog signals, but at the same time, has disadvantages in that it requires a broad bandwidth and has a complex system. Despite these disadvantages, a digital method has been widely used in these days due to relatively fewer errors, high reliability, and development of circuit technology that has been made in recent days.
In digital communication, a transmitter modulates data to be suitable for transmission prior to transmission of the data, and a receiver demodulates original data signals from transmitted signals. In general, a demodulation in the receiver can be thought as an inverse of a modulation.
Communication using digital signals is used in various fields such as wireless communication, digital broadcasting, and the like. As a modulation method in a wireless communication field, there may be used various methods such as a method of modulating only a phase such as quadrature phase shift keying (QPSK), a method of modulating a phase and an amplitude such as quadrature amplitude modulation (QAM), and the like.
In the wireless communication field, much research has been conducted for better spectral efficiency with limited resources. As one of these methods, a multiple-input multiple-output (MIMO) method may be given.
The MIMO method is based on input and output of signals using a plurality of antennas. This method is characterized in that a plurality of data streams are transmitted simultaneously on the same channel using a plurality of antennas different from each other. As the number of channels is increased, the channel capacity is increased in proportion to the number of channels, and therefore it is possible to actually improve the speed of communication link. In addition, this method has an advantage in that the channel bandwidth is not increased while improving the throughput.
However, the MIMO technique has limitations in that a plurality of antennas should be used and costs for additional devices may be required. In addition, a small device such as a mobile terminal may have a spatial limitation in its use of the plurality of antennas and an additional configuration. Moreover, interference between channels is a problem to be solved for the design of receiver.